Overpotential

About: Overpotential is a research topic. Over the lifetime, 16474 publications have been published within this topic receiving 616632 citations.

Highly Active and Stable Hybrid Catalyst of Cobalt-Doped FeS2 Nanosheets–Carbon Nanotubes for Hydrogen Evolution Reaction

Abstract: Hydrogen evolution reaction (HER) from water through electrocatalysis using cost-effective materials to replace precious Pt catalysts holds great promise for clean energy technologies. In this work we developed a highly active and stable catalyst containing Co doped earth abundant iron pyrite FeS2 nanosheets hybridized with carbon nanotubes (Fe1–xCoxS2/CNT hybrid catalysts) for HER in acidic solutions. The pyrite phase of Fe1–xCoxS2/CNT was characterized by powder X-ray diffraction and absorption spectroscopy. Electrochemical measurements showed a low overpotential of ∼0.12 V at 20 mA/cm2, small Tafel slope of ∼46 mV/decade, and long-term durability over 40 h of HER operation using bulk quantities of Fe0.9Co0.1S2/CNT hybrid catalysts at high loadings (∼7 mg/cm2). Density functional theory calculation revealed that the origin of high catalytic activity stemmed from a large reduction of the kinetic energy barrier of H atom adsorption on FeS2 surface upon Co doping in the iron pyrite structure. It is also fo...

A Strongly Coupled Graphene and FeNi Double Hydroxide Hybrid as an Excellent Electrocatalyst for the Oxygen Evolution Reaction

Abstract: Cost-effective electrocatalysts for the oxygen evolu- tion reaction (OER) are critical to energy conversion and storage processes. A novel strategy is used to synthesize a non- noble-metal-based electrocatalyst of the OER by finely com- bining layered FeNi double hydroxide that is catalytically active and electric conducting graphene sheets, taking advant- age of the electrostatic attraction between the two positively charged nanosheets. The synergy between the catalytic activity of the double hydroxide and the enhanced electron transport arising from the graphene resulted in superior electrocatalytic properties of the FeNi-GO hybrids for the OER with over- potentials as low as 0.21 V, which was further reduced to 0.195 V after the reduction treatment. Moreover, the turnover frequency at the overpotential of 0.3 V has reached 1 s 1 , which is much higher than those previously reported for non-noble- metal-based electrocatalysts. The growing demand for energy and the increasing concerns about environment pollution from fossil fuels are stimulating intense research interest in energy conversion and storage from alternative sustainable energy sources. As one of the most important process to produce and store renewable energy in chemical form, the oxygen evolution reaction (OER) has led to many studies in recent years. However, the kinetics of OER is sluggish. Therefore, an effective electro- catalyst is needed to accelerate the reaction and reduce the large overpotential and thus improve the energy conversion efficiency. Metal oxides are the most active and durable electrocatalysts for OER, among which IrO2 and RuO2 are thought to be best OER catalysts in both acidic and alkaline solutions. (1) However, the high cost and element scarcity greatly hindered the widespread use of these noble-metal oxide catalysts. Therefore, it is desirable to develop efficient alternative catalysts based on inexpensive and earth-abun- dant elements without compromising good catalytic activity and durability for OER. Recently, extensive efforts have been made to use perovskites (2) and first-row transition-metal- based materials (3) as low-cost catalysts or electrode materials

Isolated Ni single atoms in graphene nanosheets for high-performance CO2 reduction

Abstract: Single-atom catalysts have emerged as an exciting paradigm with intriguing properties different from their nanocrystal counterparts Here we report Ni single atoms dispersed into graphene nanosheets, without Ni nanoparticles involved, as active sites for the electrocatalytic CO2 reduction reaction (CO2RR) to CO While Ni metal catalyzes the hydrogen evolution reaction (HER) exclusively under CO2RR conditions, Ni single atomic sites present a high CO selectivity of 95% under an overpotential of 550 mV in water, and an excellent stability over 20 hours’ continuous electrolysis The current density can be scaled up to more than 50 mA cm−2 with a CO evolution turnover frequency of 21 × 105 h−1 while maintaining 97% CO selectivity using an anion membrane electrode assembly Different Ni sites in graphene vacancies, with or without neighboring N coordination, were identified by in situ X-ray absorption spectroscopy and density functional theory calculations Theoretical analysis of Ni and Co sites suggests completely different reaction pathways towards the CO2RR or HER, in agreement with experimental observations

Kinetics of the Deposition of Inert Particles from Electrolytic Baths

Abstract: To explain the peculiarities shown by the codeposition of inert particles from electrolytic baths, a mechanism based on two successive adsorption steps is proposed. In the first step the particles are loosely adsorbed, and they are in equilibrium with the particles in suspension. In the second step the particles are irreversibly adsorbed. Making a few elementary hypotheses about the mechanism that governs the two steps it is possible to deduce a general expression relating the concentration of the embedded particles to the suspension concentration and the electrode overpotential. This relationship is verified experimentally.

Passivating surface states on water splitting hematite photoanodes with alumina overlayers

Abstract: Hematite is a promising material for inexpensive solar energy conversion viawater splitting but has been limited by the large overpotential (0.5–0.6 V) that must be applied to afford high wateroxidation photocurrent. This has conventionally been addressed by coating it with a catalyst to increase the kinetics of the oxygen evolution reaction. However, surface recombination at trapping states is also thought to be an important factor for the overpotential, and herein we investigate a strategy to passivate trapping states using conformal overlayers applied by atomic layer deposition. While TiO2 overlayers show no beneficial effect, we find that an ultra-thin coating of Al2O3 reduces the overpotential required with state-of-the-art nano-structured photo-anodes by as much as 100 mV and increases the photocurrent by a factor of 3.5 (from 0.24 mA cm−2 to 0.85 mA cm−2) at +1.0 V vs. the reversible hydrogen electrode (RHE) under standard illumination conditions. The subsequent addition of Co2+ ions as a catalyst further decreases the overpotential and leads to a record photocurrent density at 0.9 V vs. RHE (0.42 mA cm−2). A detailed investigation into the effect of the Al2O3 overlayer by electrochemical impedance and photoluminescence spectroscopy reveals a significant change in the surface capacitance and radiative recombination, respectively, which distinguishes the observed overpotential reduction from a catalytic effect and confirms the passivation of surface states. Importantly, this work clearly demonstrates that two distinct loss processes are occurring on the surface of high-performance hematite and suggests a viable route to individually address them.